A. Field of the Invention
The invention relates to a perpendicular magnetic recording medium suitable for high-density magnetic recording.
B. Description of the Related Art
In recent years there have been mounting demands for magnetic recording media capable of higher recording densities. Lately perpendicular magnetic recording methods to perform recording with the easy axis of magnetization of the recording layer oriented in the perpendicular direction have been commercialized, and recording densities demands have increased further. High thermal stability, lower noise, and reduced magnetic spacing are necessary in order to raise recording densities. One measure to reduce the magnetic spacing is the method of making the protective layer formed on the magnetic layer thinner. However, as the protective layer is made thinner, Co elution increases. In addition, deterioration of sliding durability becomes prominent, so that reliability problems emerge. A soft magnetic backing layer is necessary in perpendicular magnetic recording methods. The Co-based alloy or other soft magnetic backing layer has a composition ratio resulting in poorer corrosion resistance than the Co-based alloy of the magnetic layer, so that in perpendicular magnetic recording, Co elution is primarily from the soft magnetic backing layer. This problem is made more serious by reduction of the thickness of the protective layer.
As an approach to prevent Co elution due to a thinner protective layer, for example, a method has been proposed in which a Pt group element other than Pt and an element with negative electrode potential are added to the magnetic layer (see for example, Japanese Patent Laid-open No. 2003-223707 (US2003138666A1)). However, methods of adding elements to the magnetic layer are thought not to have much effect for small amounts added, so that large amounts of the above elements must be added. Addition of such excessive amounts of these elements is thought to induce degradation of the magnetic characteristics and electromagnetic transducing characteristics. In particular, an element in the Pt group other than Pt has a large atomic radius, and it is thought that adjustment of the composition of a layer other than the magnetic layer, such as the intermediate layer, the underlayer or the like, or adjustment of the film deposition process, is also necessary. It is thought that elution of Co from the magnetic layer can be suppressed, but it is believed that there is no effect in reducing Co elution from the soft magnetic backing layer.
As another approach, for example, a method has been proposed using material high in corrosion resistance, in which the seed layer is formed from two layers, which are an amorphous Cr alloy and an fcc structure Ni alloy (Japanese Patent Laid-open No. 2007-184019 (US2007153419A1)).
Another method is a method of providing one intermediate layer, with passivation treatment performed, between the magnetic layer and the protective layer (see, for example, Japanese Patent Laid-open No. 8-273155). However, there is the problem that the magnetic spacing is increased by the addition of such an intermediate layer.
As still another method, a technique has been proposed in which Cr and hard minute particles are added to the protective layer (see, for example, Japanese Patent Laid-open No. 2002-100036). However, functions required of the protective layer include not only prevention of Co elution, but also durability with respect to sliding and other functions, and to limit the material to prevention of Co elution greatly hinders the object of maximizing other functions of the layer.
The present invention is directed to overcoming or at least reducing the effects of one or more of the problems set forth above.